Laser Design Research Articles

A versatile high-average-power ultrafast infrared driver tailored for high-harmonic generation and vibrational spectroscopy.

We report on an ultrafast infrared optical parametric chirped-pulse amplifier (OPCPA), pumped by a 200-W thin-disk Yb-based regenerative amplifier at a repetition rate of 100 kHz. The OPCPA is tunable in the spectral range 1.4-3.9 [Formula: see text]m, generating up to 23 W of < 100-fs signal and 13 W of < 200-fs idler pulses for infrared spectroscopy, with additional spectral filtering capabilities for Raman spectroscopy. The OPCPA can also yield 19 W of 49-fs 1.75-[Formula: see text]m signal or 5 W of 62-fs 2.8-[Formula: see text]m idler pulses with active carrier-to-envelope-phase (CEP) stabilisation for high-harmonic generation (HHG). We illustrate the versatility of the laser design, catering to various experimental requirements for probing ultrafast science.

Design of low-threshold photonic-crystal surface-emitting lasers with confined gain regions by using selective area intermixing

Photonic-crystal surface-emitting lasers have many promising properties over traditional semiconductor lasers and are regarded as the next-generation laser sources. However, the minimum achievable lasing threshold of PCSELs is still several times larger than that of VCSELs, and limiting its applications especially if the required power is small. Here, we propose a new design that reduces the gain region in the lateral plane by using selective quantum-well intermixing to reduce the threshold current of PCSELs. By performing theoretical calculations, we confirmed that the threshold current can be lowered by a factor of two to three while keeping the PCSEL’s advantage of small divergence angle.

Amplitude noise suppression in Yb:doped NALM oscillators utilizing saturable absorber settings.

Optical frequency combs based on fiber lasers mode-locked (ML) with a nonlinear amplifying loop mirror (NALM) have become the backbone of many cutting-edge applications, ranging from precision spectroscopy to quantum physics. Being extremely precise measurement tools, understanding their passive stability and low-noise operation regimes is vital. While several influences on the laser noise have been studied, many parameters remain poorly understood. Here, we systematically analyze under which preconditions the artificial saturable absorber settings of the laser can be modified during operation without losing mode-locking and the effects on laser noise, the spectrum and the output power. Our results show that it is possible to decrease the amplitude noise (AM noise) of the laser by more than 50 % by simply rotating a wave plate within the laser cavity. Additionally, we discuss differences to a similar effect observed in a NALM-alike laser amplifier and of changing the output coupling. These findings deepen our understanding and capabilities of optimizing the noise performance of ML fiber lasers, enable us to investigate new parameter spaces, and can be used to further optimize the noise performance of the NALM laser design, making it an ideal light source for advanced setups both in research and industry.

Decaying dynamics of harmonic mode-locking in a SESAM-based mode-locked fiber laser.

The entire decaying dynamics of harmonic mode-locking (HML) are studied utilizing the dispersive Fourier transform (DFT) technique in a SESAM-based mode-locked fiber laser. It is unveiled that the harmonic solitons do not disappear directly, but undergo transitional processes from the higher-order HML to the lower-order HML and then to the fundamental mode-locking (FML), and finally vanish. The "big corner" can also exist in the decaying process rather than just in the buildup process of HML, and there is at least one "big corner" during the decaying process between the consecutive multi-pulsing states. The energy stabilization phase (ESP) cannot be observed during every transitional process. A breathing behavior and a vibrating soliton molecule are observed in the decaying process from the 2nd HML to the FML and in the decaying process of the FML, respectively. Our work would enrich the understanding of HML behaviors and may contribute to the laser designs.

Atmospheric Thermodynamic Profiling through the Use of a Micro-Pulse Raman Lidar System: Introducing the Compact Raman Lidar MARCO.

It was for a long time believed that lidar systems based on the use of high-repetition micro-pulse lasers could be effectively used to only stimulate atmospheric elastic backscatter echoes, and thus were only exploited in elastic backscatter lidar systems. Their application to stimulate rotational and roto-vibrational Raman echoes, and consequently, their exploitation in atmospheric thermodynamic profiling, was considered not feasible based on the technical specifications possessed by these laser sources until a few years ago. However, recent technological advances in the design and development of micro-pulse lasers, presently achieving high UV average powers (1-5 W) and small divergences (0.3-0.5 mrad), in combination with the use of large aperture telescopes (0.3-0.4 m diameter primary mirrors), allow one to presently develop micro-pulse laser-based Raman lidars capable of measuring the vertical profiles of atmospheric thermodynamic parameters, namely water vapor and temperature, both in the daytime and night-time. This paper is aimed at demonstrating the feasibility of these measurements and at illustrating and discussing the high achievable performance level, with a specific focus on water vapor profile measurements. The technical solutions identified in the design of the lidar system and their technological implementation within the experimental setup of the lidar prototype are also carefully illustrated and discussed.

The future of photonic crystal surface-emitting lasers

Semiconductor lasers are the heart for the development of technologies in many fields. In recent decades, a new type of large-area surface-emitting lasers based on the in-plane photonic crystal modulation and feedback have emerged to show superior advantages of high output power, low-divergence, high beam quality and brightness, and compact and monolithic structure. In this paper, we review the design and development of photonic crystal surface-emitting laser and discuss the future investigation and improvements.

Determining thermomechanical response of thin disk lasers with physics-informed neural networks

Acquiring structural behavior related to thermal effects is essential to the design of high-power thin disk lasers. However, quantifying the thermomechanical response of a thin disk laser crystal (TDLC) is challenging since these variables of interest are always highly tensorial. Herein, we developed a method to directly quantify the thermo-induced structural behavior of a TDLC from scalar temperature by a physics-informed neural network (PINN). The PINN is established to approximate the unknown states (thermal displacement, strain, and stress fields) using the loss functions encoded with sparse temperature and thermal mechanics equations. Steady-state and transient results of thermo-induced structural responses are precisely obtained from the temperature field by training PINN. In addition, transfer learning is demonstrated to enhance the computation efficiency of PINN for TDLCs with various materials and geometric properties. Implanting PINNs into thin disk lasers paves the way for precise quantification of highly tensorial thermal effects of lasers in-situ using easily accessible scalars.

Brightness Prediction of Large Color Gamut Laser Display Devices.

A brightness-perceived color appearance model tailored for large gamut display devices, exemplified by laser displays, was investigated. Psychophysical experiments on the brightness matching of 30 color stimuli with achromatic white light were conducted by 16 observers. The analysis compares the performance of a number of existing color appearance models and equivalent luminance models in predicting brightness. None of the models performed acceptably due to a severe underestimation of the Helmholtz-Kohlrausch (H-K) effect. A modified model of perceived brightness based on CAM16, taking into account the H-K effect, is proposed. Evaluated by psychophysical experiments, the proposed model exhibits a superior performance compared to the preceding models, especially within the extensive color gamut range stipulated by BT.2020. The results help to optimize the design of laser displays with a wide color gamut and high perceived brightness.

Artificial neural networks for photonic applications—from algorithms to implementation: tutorial

This tutorial–review on applications of artificial neural networks in photonics targets a broad audience, ranging from optical research and engineering communities to computer science and applied mathematics. We focus here on the research areas at the interface between these disciplines, attempting to find the right balance between technical details specific to each domain and overall clarity. First, we briefly recall key properties and peculiarities of some core neural network types, which we believe are the most relevant to photonics, also linking the layer’s theoretical design to some photonics hardware realizations. After that, we elucidate the question of how to fine-tune the selected model’s design to perform the required task with optimized accuracy. Then, in the review part, we discuss recent developments and progress for several selected applications of neural networks in photonics, including multiple aspects relevant to optical communications, imaging, sensing, and the design of new materials and lasers. In the following section, we put a special emphasis on how to accurately evaluate the complexity of neural networks in the context of the transition from algorithms to hardware implementation. The introduced complexity characteristics are used to analyze the applications of neural networks in optical communications, as a specific, albeit highly important example, comparing those with some benchmark signal-processing methods. We combine the description of the well-known model compression strategies used in machine learning, with some novel techniques introduced recently in optical applications of neural networks. It is important to stress that although our focus in this tutorial–review is on photonics, we believe that the methods and techniques presented here can be handy in a much wider range of scientific and engineering applications.

Improving 2–4 μm mid-infrared fluorescence properties of Ho3+ via Er3+ energy transfer in tellurite glasses

Despite significant advancements in the field of mid-infrared lasers, the fluorescence around the 2–4 μm wavelength range remains a pressing concern. Ho3+/Er3+ co-doped TeO2–ZnO–Nb2O5–PbO (TZNP) glasses were fabricated by conventional melt-quenching technique, and we also characterized their excellent mid-infrared (MIR) fluorescence properties. According to the observed parameter ΔT (144–141 °C) > 120 °C from differential scanning calorimeter (DSC) curves, the manufactured tellurite glass specimens displayed enhanced thermal stability and crystallization resistance. X-ray diffractometer (XRD) images demonstrated the non-crystalline structure of the produced specimens. Ho3+/Er3+ co-doped tellurite glass specimens achieved emission enhancements of 2.0 μm and 4.1 μm through energy absorption of 980 nm LD, which could be assigned to the Ho3+: 5I7 → 5I8 and Ho3+: 5F5 → 5I4 radiation transition processes respectively. Meanwhile, intense 3.1 μm fluorescence was observed, which could be attributed to the transition of Er3+: 4S3/2 → 4F9/2. We investigated the fluorescence properties of the produced glasses in detail, and the processes of energy transferring between Ho3+/Er3+ were discussed on the basis of the quenching and increasing emission intensity at different dopant proportions of Er3+ ions. Additionally, the optimized 1 mol% Ho3+ and 1.5 mol% Er3+ co-doped TZNP glass possessed the strongest emission intensity, and the fluorescence lifetime values of this sample were calculated to be 1.81 ms and 1.38 ms at 2.0 μm and 4.1 μm, respectively. The gain coefficients demonstrated that only small pump energy can achieve the MIR laser gains. These above findings suggest that the prepared samples are potentially competitive and efficient as an innovative glass in the MIR laser design and optical amplifiers applications.

Passively synchronized dual-color soliton fiber laser based on single-walled carbon nanotubes

In this work, we propose a uniquely designed fiber laser to generate dual-color soliton molecules, which are stable bound states made up of solitons with different carrier frequencies, pulse widths and soliton energies. This fiber laser consists of two resonators, which are cascaded by a pair of wavelength division multiplexers (WDMs), and a single-walled carbon nanotube saturable absorber (SWCNT-SA) is placed in the common branch shared by two sub-cavities to achieve optical soliton mode-locking. The optical solitons generated by this laser have central wavelengths of 1530.43 nm and 1547.62 nm with pulse widths of 0.832 ps and 1.198 ps, respectively. The synchronous mode-locked operation of the two sub-cavities can be easily achieved by adjusting the optical delay line (DL) in one of the resonant cavities. When the synchronized state is reached, two solitons with different central wavelengths operate synchronously and stably at a consistent repetition frequency of ∼8.1505 MHz and dual-color soliton molecules are generated. The fiber laser has the advantages of simple structure and controllable generation of soliton molecules, which provide a new idea for the design of soliton molecule ultrafast fiber laser.

Design of a Broadband Erbium-Doped Fluoroindate Fiber Laser Emitting Up to 3.91 μm

In this paper, for the first time, an erbium-doped fluoroindate fiber laser emitting up to 3.91 μm is designed and optimized by means of a numerical investigation performed via a home-made computer code. It is cladding pumped with red light at 635 nm. The employed fiber is commercially available from Le Verre Fluoré and exhibits a double D-shaped geometry. Continuous-wave laser emission is obtained thanks to the population inversion between the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9/2</sub> and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9/2</sub> energy levels. The model takes into account measured spectroscopic parameters for the absorption, stimulated emission and spontaneous decay processes. The device performance is investigated by varying several parameters, such as the input pump power, the fiber length, the dopant concentration, the output mirror reflectivity and the signal wavelength. The proposed device is very versatile and is optimized for different scenarios, including: the shortest fiber, the highest output power and the lowest threshold. Simulation results show that the best performance in terms of emission bandwidth is obtained for the laser with the lowest threshold, i.e. only 25 mW, predicting a broadband coherent emission in the 3.25-3.91 μm wavelength range and paving the way to the fabrication of a low-cost and easy-to-pump middle infrared fiber laser.

Tunable random lasers via phase transition for information encryption

Introducing phase transition materials to random systems provides a promising route to create new optoelectronic functionalities of random lasers. Here, a phase transition random laser with switchable lasing modes is reported, which is designed with a thermoresponsive hydrogel as scattering medium. By manipulating the phase transition in hydrogel, random lasing modes can be switched reversibility between incoherent and coherent random lasing. The phenomenon derives from the changing of light scattering properties in different phase states, thus affecting the optical feedback path of random lasing. Besides, based on its controllable and easily detectable time-domain characteristics, the phase transition random laser is applied in information encoding and transmission. It is the first time that the transition from coherent to incoherent random lasing is observed by varying the sample phase states. This work will inspire the design and application of novel random lasers in photoelectric device.

Dual-parameter femtosecond mode-locking pulse generation in partially shared all-polarization-maintaining fiber Y-shaped oscillator with a single saturable absorber

We present a design of a mode-locked fiber laser based on a polarization-maintaining (PM) Y-shaped fiber structure, which employs a single semiconductor saturable absorber mirror (SESAM) and a common polarization beam combiner (PBC) to achieve dual- parameter mode-locking femtosecond pulse in two orthogonal polarization states. The two output pulses have different characteristics, such as repetition frequency (87.3 MHz and 91.3 MHz), average output powers (2.1 mW and 1.9 mW), pulse durations (299 fs and 377 fs) and spectral profiles (centered at 1565.6 nm and 1563.6 nm with spectral width of 9.96 nm and 9.93 nm). The properties of the two pulses are experimentally characterized and their potential applications in areas such as bistable frequency lasers and dual femtosecond optical frequency comb is discussed.

Frequency Comb Fiber Generator Based on Photonic Bandgap Amplifier

We report on a model of a fiber frequency comb generator that develops an approach to harmonically mode-locked fiber laser design based on dissipative four-wave mixing. In our version of this approach, we assume an amplifying one-dimensional photonic crystal as a key cavity element combining the properties of an intra-cavity filter and a power amplifier. Using standard equations describing the signal transformation in the ring cavity and the output fiber cascade, we have demonstrated the possibility of the application of the proposed model as a generator of broadband frequency comb with controllable line spacing.

Two-well injector direct-phonon terahertz quantum cascade lasers

We present an experimental study on a terahertz quantum cascade laser (THz QCL) design that combines both two-well injector and direct-phonon scattering schemes, i.e., a so-called two-well injector direct-phonon design. As a result of the two-well injector direct-phonon scheme presented here, the lasers benefit from both a direct phonon scattering scheme for the lower laser level depopulation and a setback for the doping profile that reduces the overlap of the doped region with active laser states. Additionally, our design also has efficient isolation of the active laser levels from excited and continuum states as indicated by negative differential resistance behavior all the way up to room temperature. This scheme serves as a good platform for improving the temperature performance of THz QCLs as indicated by the encouraging temperature performance results of the device with a relatively high doping level of 7.56 × 1010 cm−2 and Tmax ∼ 167 K. With the right optimization of the molecular beam epitaxy growth and interface quality, the injection coupling strength, and the doping density and its profile, the device could potentially reach higher temperatures than the latest records reached for the maximum operating temperature (Tmax) of THz QCLs.

Multi-dimensional multiplexed, tri-comb and quad-comb generation from a bidirectional mode-locked fiber laser.

Tri-comb and multi-comb techniques could enable many advanced measurement applications beyond the reach of traditional dual-comb schemes. However, the sophisticated and bulky control systems of the conventional schemes based on three comb lasers render them impractical for many potential applications. Like their dual-comb counterparts, tri-comb and multi-comb lasers are being investigated as attractive alternatives. In contrast to previous dual-comb lasers using only one multiplexing dimension of optical pulses, this work simultaneously leverages multiplexing methods in three physical dimensions, i.e. wavelength, polarization, and direction, to generate triple to quadruple asynchronous pulse trains in a bidirectional mode-locked fiber laser. Because of the unique cavity structure studied here, both wavelength-multiplexed and polarization-multiplexed dual-comb generation from a completely shared-cavity and wavelength/polarization-multiplexed multi-comb generation from a bidirectional partially shared-cavity are achieved. Good relative stability among the generated combs of the fiber laser is demonstrated, as well as proof-of-concept dual-comb spectroscopy measurements, which validates the mutual coherence between the combs. The analysis of the experimental results further reveals interesting performance comparisons between combs from different multiplexing schemes, thanks to the special laser design used here that allows a side-by-side dual-comb demonstrations from different combinations of outputs from the same laser. Our investigation could facilitate multi-comb generation based on one light source for field-deployable multi-comb applications.

Transient light shift register mechanism of bi-chromatic pulse generation

Primary methods for generating short pulses in lasers require intracavity elements or physical mechanisms for modulation or the saturable absorption of radiation. This often complicates laser design and limits capabilities, particularly beyond single-wavelength operation. We propose and explore a method for the synchronous generation of bicolor, high-repetition-rate pulses that combines stimulated emission from Yb rare-earth ions and Raman scattering in a shared all-fiber laser cavity, without employing saturable absorbers or modulators. The proposed mechanism for pulsed lasing is analogous to an optical shift register, with two pulse trains shifting relative to each other by one period after every round trip. This naturally solves the critical problem of compensating for the dispersion-induced differential delay of bi-chromatic pulses during an intracavity round trip. The shift register inherently enables stationary generation of bi-chromatic pulses with a common relatively high repetition rate that is inversely proportional to the differential delay. We have demonstrated the feasibility of the proposed technique through the stable generation of sub-nanosecond bi-chromatic (1066 and 1241 nm) pulses with a repetition rate exceeding 166 MHz. The proposed approach is rather general, and we anticipate that it can facilitate more affordable bi-chromatic pulse generation in a variety of laser systems.

Transient dynamics of dissipative solitons formation in a net-normal dispersion mode-locked fiber laser based on nonlinear polarization evolution.

In mode-locked fiber lasers, the formation of ultrashort pulses from noisy or unstable states is a crucial area of research. Investigating these complex nonlinear dynamics can lead to valuable insights and new practical engineering techniques, particularly for the design and optimization of optical systems. Time-stretch dispersive Fourier transform, utilized in our study to investigate dissipative solitons formation in a net-normal dispersion nonlinear polarization evolution mode-locked fiber laser, provides a window into the intricate dynamics of such systems. In our experiments, the identification of five distinct transient stages in the formation process sheds light on the underlying mechanisms of dissipative soliton (DS) formation. The five distinct transient stages involved in the formation process include relaxation oscillation, modulation instability, spectral broadening, soliton explosions (SEs), and stable mode-locking. Notably, we also observed the generation of dissipative rogue waves during the SE stage. Our findings shed light on the intricate dynamics of DS formation and offer valuable insights for the design and optimization of mode-locked fiber lasers.

Advanced Solid-State Lasers: feature issue introduction

This Joint Issue of Optics Express and Optical Materials Express features 40 peer-reviewed articles written by authors who participated in the Advanced Solid State Lasers Conference, part of the Optica Laser Congress and Exhibition held in Barcelona, Spain from December 11-15, 2022. This review provides a brief summary of these articles covering the latest developments in laser host and nonlinear crystals, structured materials, fiber lasers and amplifiers, ultrafast mode-locked lasers and optical parametric amplifiers, frequency-doubled Raman lasers, vortex beams, and novel concepts in laser design.